This invention is directed to developer compositions and more specifically to liquid developer compositions containing dyes. In one embodiment, the present invention is directed to liquid developer compositions comprised of resin particles, olefin soluble dyes, preferably dyes that are soluble in the resin and insoluble in the selected carrier liquid, such as Isopar. Also, the present invention is directed to postively charged or negative charged liquid inks where charge directors such as barium petronates, lecithin and the like are selected to permit negatively charged inks, and charge directing components, such as zirconium octoate, iron naphthenate, and a polyisobutylene based polyester are selected to permit positively charged inks. The economical liquid inks of the present invention can be selected for the development of images in various imaging processes, including the liquid developer processes described in U.S. Pat. No. 3,084,043, the disclosure of which is totally incorporated herein by reference; xerographic processes, electrographic recording, electrostatic printing, and facsimile systems; color proofing processes; and the process as illustrated in British Patent Publication 2,169,416, published July 9, 1986, and U.S. Pat. No. 4,794,651, the disclosures of which are totally incorporated herein by reference.
Development of electrostatic latent images with liquid developer compositions comprised of, for example, a dispersion of pigments in a liquid hydrocarbon is known. In these methods, the electrostatic latent image, which is usually formulated on a single sheet of photoconductive paper, such as zinc oxide, is transported through a bath of the aforementioned liquid developer. Contact with the liquid developer causes the charged pigment particles present therein to migrate through the liquid to the zinc oxide sheet in the configuration of a charged image. Thereafter, the sheet is withdrawn from the liquid developer bath with the charged pigment particles adhering to the electrostatic latent image in image configuration. The thin film of residual developer remaining on the surface of the sheet is then evaporated within a relatively short time period, usually less than 5 seconds. Also, the marking pigment particles may be fixed to the sheet by heat, for example, in image configuration.
In a patentability search report, the following prior art was recited, all U.S. Pat. Nos. 3,743,503 directed to liquid developers comprised of an electrically insulating organic carrier liquid having dispersed therein marking particles comprised of polymeric dye having a linear backbone chain to which are attached pendant side chains containing a chromophoric moiety, reference the Abstract of the Disclosure, for example; 4,384,036 which describes a process for preparing a liquid developer wherein fine polymer particles are dispersed in a nonpolar solvent mixed with a dye that is insoluble in the nonpolar solvent in which is soluble in the monomer which is at least one component of the polymer, and thereafter the polymer particles are colored by removing from the dispersion a second solvent which dissolves the dye and which is apparently capable of swelling at least part of the polymer, reference the Abstract of the Disclosure; 4,476,210, mentioned herein, which illustrates a stable liquid developer with colored dyes being imbibed into a thermoplastic resin core, reference the Abstract of the Disclosure, for example; 4,636,452 directed to a method for preparing a resin dispersion containing resin particles dispersed in a high insulating hydrocarbon medium, which comprises a first polymer dissolved in the medium in which liquid toner may contain colorant such as dyes, reference column 5, beginning at line 25; 3,272,644 directed to development of latent images with crystalline toners wherein there is dispersed a dye in a crystalline carrier material, and wherein liquid developers are disclosed with such materials, see column 2, beginning at line 21; and as collateral or background interest, some of which teach the use of dyes and liquid developers, 3,296,140; 3,301,698; 3,692,520; 3,781,208; 3,849,165; 4,059,444 and 4,264,699.
There are disclosed in U.S. Pat. No. 3,554,946 liquid developers for electrophotography comprised of a carrier liquid consisting of a hydrocarbon, negatively electrostatically charged toner particles dispersed in the carrier liquid, and a pigment therein such as carbon black, aniline black, prussian blue, phthalocyanine red, and cadmium yellow. In accordance with the teachings of this patent, a copolymer is coated on the surface of the pigment particles for the primary purpose of imparting a negative electrostatic charge to these particles. Other patents disclosing similar liquid developer compositions include U.S. Pat. Nos. 3,623,986; 3,625,897; 3,976,583; 4,081,391 and 3,900,412. In the '412 there is specifically disclosed a stable developer comprised of a polymer core with a steric barrier attached to the surface of the polymer selected. In column 15 of this patent, there are disclosed specfic colored liquid developers. Attempts to obtain useful color liquid developer compositions by the ball milling process described in the '412 patent have been substantially ineffective, particularly with respect to obtaining developed images of acceptable optical density in that, for example, the desired size for the latex particles is from 0.2 to 0.3 micron in diameter; and with ball milling techniques, it is very difficult to provide a dispersion of carbon black or other pigment particles much smaller in size than about 0.7 to about 0.8 micron.
Additionally, there are described in U.S. Pat. No. 4,476,210, the disclosure of which is totally incorporated herein by reference, liquid developers containing an insulating liquid dispersion medium with submicron size marking particles therein, which particles are comprised of a thermoplastic resin core substantially insoluble in the dispersion, an amphipathic block or graft copolymeric stabilizer irreversibly chemically or physically anchored to the thermoplastic resin core, and a colored dye imbibed in the thermoplastic resin core. There is also illustrated in this patent the use of zirconium octoate as a positive charge control agent with a vinyl resin and Isopar.RTM.. The history and evolution of liquid developers is provided in the '210 patent, reference columns 1 and 2 thereof.
Also of interest are U.S. Pat. Nos. 3,869,397, which discloses the use of zirconium octoate as a negative charge control agent for a carbon black pigment in a vinyl resin, and 3,939,087, which illustrates for example a liquid developer comprising a pigment, and dye and polymer with zirconium octoate in Ispoar.RTM., which octoate can apparently function as a charge director.
In addition, there are illustrated in the aforementioned British Patent Publication 2,169,416, and U.S. Pat. No. 4,794,651 liquid developer compositions comprising toner particles associated with a pigment dispersed in a nonpolar liquid, and wherein the toner particles are formulated with a plurality of fibers or tendrils from a thermoplastic polymer, and carry a charge of polarity opposite to the polarity of the latent image. These toners apparently permit, in some instances, excellent transfer efficiencies, and exhibit excellent copy quality.
There is illustrated in Japanese Laid Open as Kokai 238581/87 on Oct. 19, 1987, the disclosure of which is totally incorporated herein by reference, stable black submicron liquid developer comprised of an insulating liquid medium having dispersed therein black marking particles comprised of a thermoplastic resin core, which is substantially insoluble in the dispersion medium, and chemically or physically anchored to the resin core an amphipathic block or graft copolymer steric stabilizer, which is soluble in the dispersion medium; and wherein dyes comprised of a specific mixture are imbibed in the thermoplastic resin core with the mixture of dyes being dispersible at the molecular level, and therefore soluble in the thermoplastic resin core and insoluble in the dispersion medium.
Other U.S. patents of interest include U.S. Pat. No. 4,210,805, which discloses toner particles prepared by adding a solvent solution of polyvinylcarbazole to Isopar.RTM. wherein the diameter of the particles is a function of the ratio of solvent to Isopar.RTM., reference column 8; U.S. Pat. No. 4,032,463 which illustrates that the ratio of toluene to Isopar.RTM. effects toner resin particle size; and U.S. Pat. No. 3,766,072 which appears to disclose that resin solvency in the vehicle effects the particle size. Also, in the '463 and '072 patents it is indicated that a solvency increase of the dispersion medium provides a larger final size particle. This occurs, it is believed, because one of the liquids used in formulating such developers is a solvent for the resin that is used. Consequently, the particle will be swollen by the entrapped solvent in the particle yielding a larger particle size. Also, in the polymerization process changing the solvent/nonsolvent ratio of the dispersion medium changes the kinetics and thus the mechanism by which particles are formed. With latex particle polymerization in hydrocarbon media, usually only submicron size particles are envisioned, reference for example "Dispersion Polymerization in Organic Media", ed. K. E. J. Barrett, Academic Press, 1975. However, it has recently been disclosed, reference M. A. Winnik, R. Lukas, W. F. Chen, P. Furlong, and M. D. Croucher, Makromol. Chem., Makromol. Symp. 10/11, 488, (1987), that by varying the solvent/nonsolvent ratio of the dispersion medium for the polymer particle being formed that the particle size may be altered and particles up to 15 microns diameter may be formed. The advantage of this technique for liquid developers has been described in U.S. Pat. No. 4,789,616, the disclosure of which is totally incorporated herein by reference.
Although the above described liquid inks are suitable in most instances for their intended purposes, there remains a need for other liquid developers, including inks which can be positively charged enabling their utilization, for example, with layered imaging members which are negatively charged, reference U.S. Pat. No. 4,265,990, the disclosure of which is totally incorporated herein by reference. There is also a need for negatively charged inks which can be selected for imaging and printing processes wherein inorganic imaging members including chalcogenides, such as selenium, selenium alloys, doped selenium substances, and doped selenium alloys, including specifically selenium arsenic, selenium tellurium, selenium tellurium arsenic, and the like optionally doped with from, for example, about 200 to about 500 parts of a halogen such as chlorine can be selected. Additionally, there is a need for liquid inks containing dyes soluble in the resin binder and insoluble in the carrier component, such as Isopar.RTM.. Furthermore, there is a need for liquid ink compositions with transfer efficiencies from imaging members to paper of greater than 95 percent and which possess reflection optical densities between about 1.1 and about 1.4 for black solid areas, and between about 0.9 and about 1.2 for colored images. Additionally, there is a need for liquid developer compositions that can be selected for a number of imaging processes including those illustrated in U.S. Pat. Nos. 3,084,043; 4,794,651, and British Publication 2,169,416 (corresponds to the aforementioned '651 patent), the disclosures of which are totally incorporated herein by reference. One main advantage associated with the liquid compositions of the present invention resides in the dye being molecularly dispersed in the resin selected rather than existing in clumps of aggregated molecules as is the situation when pigments are utilized rather than dyes. Another advantage associated with liquid developers containing dyes resides in the formation of brighter clearer colors on paper. These developer compositions wherein the dyes are, for example, molecularly dispersed in a resin can also be selected for the generation of excellent colored images on transparencies. Moreover, color mixing of the different dye based inks of the present invention are more easily achieved as compared to pigment based inks. In an embodiment of the present invention, dyes compatible with the resin can be selected as contrasted to inks with pigments wherein substantially any pigment may be selected, some of which are not compatible with the resin. There is also a need for ink compositions wherein a common charge director can be utilized with different colored dyes primarily since the toner resin is believed to be the dominant factor in controlling the charging properties. Also, with common charge directors economical advantages are achievable.
Another specific need resides in the provision of economical, excellent light fastness liquid developers with olefin soluble dyes as colorants rather than pigments wherein the aforementioned colorant is molecularly dispersed in the resin rather than existing in clumps of aggregated molecules.